1. Field of the Disclosure
The present disclosure relates to a semiconductor laser, and more particularly, to a high-power optically end-pumped external-cavity semiconductor laser capable of allowing a pumping laser beam to be directly incident from a rear of a laser chip through a micro-lens integrated heat sink.
2. Description of the Related Art
Vertical cavity surface emitting lasers (VCSELs) employ single longitudinal oscillations of very narrow spectrums of light to emit beams having small projection angles. Thus, the coupling efficiency of VCSELs with optical fibers is high and VCSELs can be easily integrated with other devices when forming the surface emitting structures thereof. As a result, VCSELs are suitable as light sources of displays.
However, VCSELs commonly must have oscillation areas of 10 μm or less to make possible single longitudinal operations. However, even in this instance, VCSELs are changed from having single longitudinal states of light into having multiple longitudinal states of light as the result of the thermal lensing effects caused by increases in optical power. Thus, the maximum power of VCSELs in the single longitudinal state commonly does not exceed 5 mW.
Vertical external-cavity surface emitting lasers (VECSELs) have been suggested as a solution which could retain the advantages of VCSELs and make possible high power operations. In VECSELs upper distributed Bragg reflectors (DBRs) can be replaced with external mirrors to increase the gain areas so as to obtain a power of 100 mW or more. Surface emitting lasers have smaller gain volumes than edge emitting lasers and thus it is difficult to obtain sufficiently high gains in such surface emitting lasers. In order to address this disadvantage, VECSELs having periodic gain structures in which quantum wells (QWs) are arranged periodically have been developed. Also, there are limitations in uniformly injecting carriers into large areas using electric pumping. Thus, VECSELs having structures which uniformly pump over wide areas by optical pumping have been developed so as to obtain high powers.
A conventional VECSEL includes a pumping unit supplying a pumping laser beam, a laser chip pumped by the pumping laser beam in order to emit a laser beam, and an external mirror installed outside the laser chip constituting an external cavity resonator.
The pumping unit includes a pumping light source and a collimating lens condensing the pumping laser beam radiated from the pumping light source.
However, in the structure of the pumping unit, the distance from the pumping light source to the laser chip is half of an entire length of the VECSEL. Thus, there are limitations when attempting to reduce the size of a VECSEL module. Accordingly, it is difficult to modularize the VECSEL to a compact size of several to tens of millimeters.